PI3 kinases are a family of lipid kinases that have been found to play a key role in the regulation of many cellular processes including proliferation, survival, carbohydrate metabolism, and motility. PI3Ks are considered to have an important role in intracellular signal transduction. In particular, the PI3Ks generate and convey signals that have important roles in cancer. PI3Ks are ubiquitously expressed, are activated by a high proportion of cell surface receptors, especially those linked to tyrosine kinases, and influence a variety of cellular functions and events. Although some PI3K activity is likely to be essential for cellular health, PI3Ks are a diverse group of enzymes for which there is increasing evidence of functional specialization. This opens up the possibility of developing isoform-selective inhibitors that can be used to treat cancer.
The primary enzymatic activity of PI3K is the phosphorylation of inositol lipids (phosphoinositides) on the 3-position of the inositol headgroup. PI3 kinases catalyze the addition of phosphate to the 3′-OH position of the inositol ring of inositol lipids generating phosphatidyl inositol monophosphate, phosphatidyl inositol diphosphate and phosphatidyl inositol triphosphate.
There are a total of eight mammalian PI3Ks, which have been divided into three main classes on the basis of sequence homology, in vitro substrate preference, and method of activation and regulation. Enzymes of a first class (Class I) have a broad substrate specificity and phosphorylate phosphatidylinositiol (PtdIns), PtdIns(4)P and PtdIns(4,5)P2. Class I PI3 kinases include mammalian p110α, p110β, p110δ and p110γ. Different members of the PI3-kinase family generate different lipid products. To date, four 3-phosphorylated inositol lipids have been identified in vivo. These lipids are bound by proteins that contain the appropriate lipid recognition module and which either act as effectors or transmit the PI3K signal onwards. The most familiar form of PI3K is a heterodimeric complex, consisting of a 110 kDa catalytic subunit now known as p110α and an 85 kDa regulatory/adapter subunit, p85α.
Phosphatidylinositol 3-kinase-alpha (PI3Kα), a dual specificity lipid and protein kinase, is composed of an 85 kDa regulatory subunit and a 110 kDa catalytic subunit. The protein includes a catalytic subunit, which uses ATP to phosphorylate PtdIns, PtdIns(4)P and PtdIns(4,5)P2. PTEN, a tumor suppressor, can dephosphorylate phosphatidylinositol (3,4,5)-trisphosphate (PIP3), the major product of PI3 kinase Class I. PIP3, in turn, is required for translocation of protein kinase B (AKT1, PKB) to the cell membrane, where it is phosphorylated and activated by upstream kinases. The effect of PTEN on cell death is mediated through the PI3Kα/AKT1 pathway.
PI3Kα has been implicated in the control of cytoskeletal reorganization, apoptosis, vesicular trafficking and proliferation and differentiation processes. Increased copy number and expression of the p110α gene (PIK3CA) is associated with a number of cancers such as ovarian cancer, cervical cancer, breast cancer, colon cancer, rectal cancer, endometrial cancer, stomach cancer, liver cancer, lung cancer, thyroid cancer, acute myelogenous leukemia (AML), chronic myelogenous leukemia (CML), and glioblastomas. In view of the important role of PI3Kα in biological processes and disease states, inhibitors of this protein kinase are desirable. The present invention provides PI3K inhibitors, particularly PI3Kα inhibitors, which are useful for treating PI3Kα-mediated diseases and conditions.